I know a copy-paste of other's source code isn't legal, but what's the smallest scale for me to avoid this?

Really it depends on the license, if you find the code online either there's clearly a license attached to it or it can be considred public domain, just make sure to give credit where it's due and read the fineprint and you should be fine.

As Digital Delusion said, most sources are distributed under a certain license. You can find a description of some common open-source licenses here.

Generally, companies own all rights to code written by their employees, so if your code is from a company and doesn't have an associated license, I'm guessing that you won't be able to use the code without written permission.

Websites that offer cut and paste code often have a usage section, detailing the license that the code is under in most cases it's public domain or under a 'acknowledgement' type license (eg: you make no claim to have written the code and acknowledge the author), but some are different so you will need to check with the site or person you got the code from.

Never ever try and claim you wrote code that you didn't, it could land you in sticky water should someone dispute you ;)

The best way to 'copy' someone's code is understand the theories and ideas behind their method and implement it in your own way. This doesn;t mean, however, that you can cut-paste the code and change the variables to make it look like your own.

In short, I wouldn't copy-paste source code unless I knew and understood the exact license it is under. If in doubt, leave it out ;)

Quote: Original post by sambsp
I know a copy-paste of other's source code isn't legal, but what's the smallest scale for me to avoid this?

Zero. Copying any code in this way would be breach of copyright, unless you were quoting it in an article or book for the purpose of review or critisism.

Will they catch you if you only copy a tiny piece? It is unlikely, but that doesn't make it legal.

Quote: Original post by DigitalDelusion
Really it depends on the license, if you find the code online either there's clearly a license attached to it or it can be considred public domain,

This last part is completely wrong. Nothing can ever be considered public domain just because you found it on the internet (or anywhere else). Something is only public domain if the copyright owner explicitly states that it is (usually by stating so in an accompanying notice/license). If there is no notice/license then you must assume that it ISN'T public domain and you must seek permission from the copyright owner before it can be used.